Generally, in the storage and removal of semi-solid material from a reservoir or settling tank, it is important to know the extent of material accumulation and to regulate its removal. This is especially true in the field of waste disposal, where it is desirable to sense the level of sludge that accumulates on the bottoms of reservoirs utilized in sewage treatment plants. In most sewage disposal processes sewer effluent is eventually placed in a large tank or reservoir, in order that solid material suspended therein may settle out. When the sludge accumulates to a preset level, a pump is actuated and some sludge is pumped out and the level is thereby reduced. Heretofore, one technique for detecting the sludge level included an "electric-eye" type sensing device. However, such optical systems require continual cleaning to maintain the device operative. Also such a device must necessarily be submerged to a selected depth of operation, which makes cleaning and the regulation of sludge levels a time-consuming operation.
It is therefore a primary object of the present invention to provide a substantially maintenance-free sludge level detecting apparatus.
Another important object of the invention is to provide a system which includes a component submerged just below the surface of the fluid medium.
Still another significant object of the invention is to provide an apparatus which is selectively adjustable to detect a plurality of sludge levels, and to control an output function upon the sensing of a particularly selected sludge level.
Yet another important object of the invention is to provide continual monitoring of the sludge level, together with means for visually displaying the detected level.